The process, used widely for in situ recovery of bitumen in Canada, from the Athabasca or similar deposits, is SAGD.
But, SAGD has the following problems:
Steam is Costly
The process uses a considerable amount of water (0.25 to 0.50 bbl/bbl.bit.) even after recycle of produced water.
CO2 emissions are high (˜0.08 tonnes CO2/bbl bitumen).
CO2 emissions are not easily captured (diluted in flue gas).
Steam cannot be economically transported for more than 5 km; so a central steam plant cannot service a wide land area.
Reservoir in-homogeneities (including lean zones) can negatively impact SAGD performance.
Temperature is fixed by operating pressure. T cannot exceed saturated-steam temperatures. If we have to lower pressures, to help contain reservoir fluids, productivity is reduced.
SAGD cannot mobilize connate water by vaporization.
Produced water volumes are less than injected steam volumes, usually.
SAGD cannot reflux steam in the reservoir—it is a once-through steam process.
Well-bore hydraulics can limit effective well lengths to <1000 m using normal well sizes and a 5 m spacing between injector and producer.
SAGD cannot mobilize lean-zone water by vaporization. Lean zones, with reduced bitumen saturation, can block steam chamber growth and impair productivity.
SAGD, in the steam-swept zone, leaves behind residual bitumen (10-25%) that is not recovered.
SAGDOX may be defined herein with respect to the present invention as a SAGD add-on process that utilizes oxygen in addition to the steam used with SAGD and which mixes together to inject energy (heat) to the bitumen. Oxygen provides additional heat by combusting residual bitumen in a steam-swept zone. A SAGDOX process may be initiated as well without SAGD.
Implementing a SAGDOX process is capable of reduce the overall cost of energy delivered to the bitumen reservoir.
SAGDOX should use less water directly, and produces more water than used when accounting for connate water, combustion water and lean zone water.
CO2 is emitted in a concentrated stream, suitable for sequestration.
If some CO2 is sequestered in the reservoir or sequestered in an off-site location, SAGDOX can emit less CO2 than SAGD.
Oxygen can be economically transported in pipelines for over a 100 miles. We can centralize oxygen production.
A SAGDOX process will not be affected, as much as SAGD, by reservoir in-homogeneities.
In a SAGDOX process, the combustion component of energy delivery creates temperatures higher than saturated-steam T. For a given reservoir or process pressure, SAGDOX will have higher average T than SAGD.
Connate water will be vaporized and mobilized as steam in SAGDOX.
Since average SAGDOX T is greater than saturated steam T, we can reflux some steam in the reservoir.
Per unit production, produced fluid (bitumen+water) volumes are less than SAGD volumes, so we can extend the length of the horizontal production well without exceeding hydraulic limits.
A single well pair for a SAGDOX process can recover more oil than a comparable SAGD well pair.
Lean zone bitumen will be recovered or combusted, lean zone water will be vaporized.
Almost no recoverable bitumen will be left behind in the combustion-swept zone.
Literature Studies
Oxygen ISC has been studied and practiced for many years (but not in bitumen reservoirs). But, there is a lot of work focused on steam+oxygen mixtures. Over a 30 year span, there are 4 relevant studies, as follows:
Steam+CO2—after oxygen reacts in the reservoir, the “working fluid” is a steam+CO2 mixture. In the early 1980's (Balog, Kerr and Pradt, OGJ, 1981), a study of steam+CO2 injection for cyclic steam EOR (CSS) was carried out. The steam+CO2 mix was produced by a WAO boiler, but the mix could also be produced, in situ, by injection of a steam+O2 mix. The mix contained about 9% (v/v) CO2 in steam, equivalent to a steam+O2 mix containing about 12% O2. We used a Calgary simulation consultant (Intercomp) to model Cold Lake CSS. After 3 CSS cycles, the key simulations results were:                bitumen productivity improved by 35 to 38% compared to steam-only injection        oil-to-steam ratio (OSR) improved by 49 to 57%        productivity pre-unit-energy-injected improved by 30 to 37%        
Carbon dioxide (non-condensable gas) improved CSS performance by providing gas drive assist in the “puff” part of the CSS cycle. Cold Lake reservoir fluids also absorbed CO2. Carbon dioxide retention (ie sequestration) was considerable—70 MMSCF alter 3 cycles (1.8 MSCF/bbl bitumen produced). This volume (1.8 MSCF/bbl) is greater than CO2 produced in SAGDOX (9) and about ⅔ CO2 produced by SAGDOX (35).
Combustion Tube Tests—(“Parametric Study of Steam Assisted Insitu Combustion” R. G. Moore et al, Feb. 23, 1994 (U of C). Now, lets shift forward by 13 years. In the early 1990's a consortium of companies and government studied combustion tube behaviour of steam/oxygen mixes compared to dry and wet ISC. The crude oil (bitumen) and cores were from Primrose. The tests were conducted at U of C's combustion laboratory. Virgin cores and pre-steamed cores were used (pre-steamed cores were to simulate reservoir combustion where the reservoir had been previously swept by steam). Four combustion process types were evaluated:                steam/O2 mixes with O2 at 2, 6 and 12 (v/v) %        dry combustion using air        conventional wet combustion (small amounts of water)        super-wet combustion (large amounts of water)        
The results were presented by a series of graphs, where the type of process was labeled by numbers. This makes interpretation difficult. But, the results/conclusions include the following:                Super—wet combustion (liquid water injection, with a water/O2 ratio of 10-15 kg/m3) exhibited LTO and was deemed unsuitable for ISC.        Conventional net combustion, dry ISC (air) and dry ISC (O2) showed good HTO and are suitable for ISC.        SAGD and oxygen addition showed good oil recovery.        Oxygen used varied from about 20 to 60 sm3/m3 or from 110 to 340 SCF/bbl.        Peak (combustion) temperatures varied from about 550 to 650° C. (1020 to 1200° F.; F4.7, F4.12).        SAGD and oxygen combustion was almost complete, with (CO2+CO)/(CO) ratios varying at 12 to 14, much better than conventional combustion (6 to 12). This translates to 91.7 to 92.9% of carbon converted to CO2 for SAGD and oxygen, vs 83.3 to 91.7% for conventional combustion.        Ignition was easy. Steam preheated the core so that auto ignition occurred quickly.        The SAGD oxygen mixes actually spanned or exceed the water levels of super-wet ISC the difference was that SAGDO and oxygen injected steam, while super-wet ISC injected water.        Oxygen requirements for SAGD were inversely proportional to O2 levels in steam (not surprising?)        The SAGD and oxygen test with the lowest oxygen content exhibited some anomalous behaviour.        
Although the test results are somewhat difficult to interpret, they are very positive for SAGD and oxygen, as summed up by the following quotes directly from the report:                “The co-injection of the steam and oxygen appeared to have considerable merit, based on the stability of the combustion process over a wide range of steam/oxygen ratios” [in a separate conversation G. Moore noted that steam/oxygen combustion was the most stable he had ever seen]        “It [steam+oxygen] offers the possibility of a new method of producing bitumen and heavy oil using the combined injection of steam and oxygen”        
SAGD and oxygen Hybrid—Now we'll shift forward by another 15 years. In 2009 U of C published a simulation study of steam/oxygen mixtures for SAGD EOR (“Design of Hybrid Steam—ISC Bitumen Recover Process”, Yang and Gates, Nat. Resources Research, Sep. 3, 2009). The simulation study used a modified STARS model, based on Athabasca reservoir operating at 4 MPa (at an over pressure) in a confined/contained model with no “leakage”. The steam/O2 injection rate was controlled (in the model) to maintain the target pressure. Steam-oxygen mixtures varied from 0% (normal SAGD) to 80% oxygen. The results/observations of the results are as follows:
Compared to Long Lake and our SAGDOX proposal herein, the study had 3 “flaws”—firstly, the steam—O2 mixtures were too rich (20, 50, 80% (v/v) oxygen) compared to our range (9.35% O2). At 80% oxygen, about 98% of the energy injected comes from O2 combustion, so the hybrid process is biased (too much) toward ISC(O2). Secondly, the reservoir GD chamber was “contained” with no “leaks” or no well to remove non-condensable combustion gases. So, using the process controls built in to the model, CO2 gas build up in the reservoir impairs injectivity and reduces productivity. Productivity plots are not based on equal energy injection. Thirdly, the U of C group focused on an “energy” usage that consisted of steam heat content and energy needed to produce/compress O2 gas. There was no consideration of energy derived from oxygen combustion. There were no plots of productivity for equal energy inputs.
Based on the kinetic combustion model in the simulator (a pseudo-component kinetic model) and other STARS systems, the bitumen and GD chamber exhibited complex behaviour with elements that are normally seen in a ISC process, as follows:                a combustion-swept zone with no residual bitumen        a bank of heated bitumen        a steam-swept zone with residual bitumen at about 25% saturation        
Carbon dioxide from combustion diluted the steam reducing steam partial pressure, lowering steam T and increasing steam-swept bitumen levels to 25% (compared to “expected” levels of 10-15%).
The average T of the combustion zone was about 450-550° C.—indicating good HTO combustion (combustion tube was 550-650° C.).
Oxygen to bitumen ratios were in the range of 200-240 sm3/m3 or 1120 to 1350 SCF/bbl.
Water use was cut dramatically compared to SAGD because of the energy released by oxygen consumption and water produced via fuel oxidation in-situ.
Apparent bitumen productivity was 25 to 40% lower than SAGD due to injectivity limitations due to CO2 build up in the contained chamber without leaks or gas removal.
There was no discussions of CO2/CO ratios in the reservoir, although the paper did say (using a kinetic model) that CO2/CO ratios of 8.96 are expected for HTO of coke (90% oxidation of carbon to CO2). (Combustion tube tests predict 92 to 93% conversion of carbon to CO2).
The group also modelled a WAG-type process, using alternating slugs of steam and oxygen injection. This process showed promise, but if ignition is ever a concern, it is probably not a good idea, in practice.
An “energy”/bitumen plot was presented, with decreasing unit “energy” for SAGD and oxygen vs. increasing energy use for SAGD. This is very misleading since the “energy” used is the energy to produce/compress oxygen+the energy in steam. It does not include the combustion energy released to the reservoir
The SI-ISC process—(SAGD-initiated insitu combustion) is currently (2010) under development by ARC (the AACI program) and supported by Nexen. The idea is to use a traditional SAGD geometry to start up (transition) to ISC. The proposed process retains the SAGD production well to produce bitumen. In one version, a new VT well is drilled at the toe of the SAGD well pair to inject air and the SAGD injection well is converted to a combustion gas production well. In another version, the VT well at the SAGD toe is used to produce combustion gases and the SAGD injector is converted to an air injector. Nexen has use rights for the SI-ISC process.
Although the process may appear to be similar to SAGDOX, we have the following distinguishing features:                the use of oxygen (not air) is not contemplated        the simultaneous injection of steam+oxygen (or air) is not contemplated        no synergies between air/oxygen and steam are contemplated        
The above demonstrates that people are considering both steam EOR (SAGD) and ISC for bitumen. The benefits for ISC are compelling, particularly for an end-of-run process.
Literature Summary
There is a paucity of R+D in this area. Only 4 studies are noted herein over a 30 year period.
But, use of oxygen in ISC has been considered for many years, going back to the 1960's (ie 50 years) the risk of LTO and injectivity difficulty into bitumen reservoirs has deterred many.
Few have contemplated the use of O2/steam mixtures.
There have been several field tests of dry ISC using oxygen.
The U of C combustion tests (1994) show superior combustion properties for steam+O2 compared to dry ISC or wet ISC processes. Combustion ignition, stability. Good bitumen recovery.
The steam+CO2 CSS simulation shows some benefits for CO2 (combustion product gas) and the prospects for some CO2 sequestration.
The U of C simulation study (2009) shows it is possible to model SAGDOX processes, and we can expect complex behaviour in our GD chamber.
The AACI tests (2010) indicate renewed interest in ISC.
It is therefore a primary object of the invention to provide a SAGDOX process wherein oxygen and steam are injected separately into a bitumen reservoir.
It is a further object of the invention to provide at least on well to vent produced gases from the reservoir to control reservoir pressures.
It is yet a further object of the invention to provide extended production wells extending a distance of greater than 1000 meters.
It is yet a further object of the invention to provide extended production wells extending a distance of greater than 500 meters.
It is yet a further object of the invention to provide oxygen at an amount of substantially 35% (v/v) and corresponding steam levels at 65%.
It is yet a further object of the invention to provide oxygen and steam from a local cogeneration and air separation unit proximate a SAGDOX process.
Further and other objects of the invention will be apparent to one skilled in the art when considering the following summary of the invention and the more detailed description of the preferred embodiments illustrated herein.